The present invention relates to a process and nozzle for feeding molten metal to the mold of a caterpillar track type mold and, more particularly, a process and nozzle for feeding molten metal wherein the distance of the nozzle from the moving mold belts is regulated during the casting operation.
One of the most difficult problems encountered in continuous casting, in particular in casting ferrous and non-ferrous metals, is the design of feeder nozzles by means of which the molten metal is introduced into the mold between the moving mold belts of a caterpillar track type mold. In the case of a caterpillar track type casting machine relatively thin strips are cast, that is, strips of 20 mm thickness and less. Accordingly the nozzles must be of relatively small dimensions especially in the region of the nozzle's mouthpiece.
There are considerable damage risks involved with the nozzles because of the very high temperature of the metal flowing through the nozzle. Only a few materials can withstand erosion or dissolution in the metal. One of the few materials which meet these requirements is graphite. Graphite, however, suffers from the disadvantage of high thermal conductivity which results in the heat is conducted away so quickly from the melt that the metal has a tendency to solidify in the nozzle.
Another suitable refractory material used widely in casting aluminum is a mixture of 30% diatomaceous earth (almost pure silica in the form of microscopic cells), 30% long asbestos fibers, 20% sodium silicate (dry mixture) and 20% chalk (to form calcium silicate). For casting steel nozzles made of ZrO.sub.2 or ZrSiO.sub.4 are generally employed.
The nozzles must withstand not only thermal stresses which arise due to the temperature of the metal being cast but also must withstand the resultant chemical attack and the mechanical stresses due to fluctuating movements of the mold belts and bending of the nozzle due to the relatively large weight of the melt passing through it. The bending leads to friction between the nozzle and the mold belts and thus to destruction of the nozzle.
Disclosed in the Swiss patent CH-PS 508 433 is a feeding nozzle which features, on the outside close to the outer edge of the nozzle, inserts which run around the whole periphery thereof. The inserts are made of a self-lubricating material. These inserts project sufficiently beyond the surface of the nozzle that they prevent any direct contact between the nozzle surface and the mold belts and prevent the molten metal from penetrating the small clearance gap between the nozzle and the mold belts. It has been found that traces of the graphite inserts rub off and behave as "activated" strips which produce faster solidification and a corresponding non-uniform structure, often resulting in surface cracks on the cast strip.
Accordingly, it is the principal object of the present invention to develop a process for use with a caterpillar track type mold which counters the mechanical bending of the nozzle and thus rubbing of the nozzle on the mold belts.
It is a further object of the present invention to develop a nozzle which is suitable for carrying out the foregoing process.